The present invention relates to the field of implantable electrodes, and more particularly to a multicontact electrode array. In a preferred embodiment, such multicontact electrode array is used with an implantable stimulator to provide electrical stimulation to body tissue, for example, to brain tissue for brain stimulation, to selected nerves for neural stimulation, or to the spinal cord for spinal cord stimulation (usually done to control or manage pain). Additionally, the present invention further provides a simple and reliable method of constructing a multicontact electrode array.
Spinal cord and other stimulation systems are known in the art. For example, U.S. Pat. No. 3,724,467, teaches an electrode implant for the neuro-stimulation of the spinal cord. A relatively thin flexible strip of physiologically inert plastic is provided as a carrier on which a plurality of electrodes is formed. The electrodes are connected by leads to an RF receiver, which is also implanted, and which is controlled by an external controller.
In U.S. Pat. No. 5,458,629, a method of making an implantable ring electrode is taught. The method disclosed in the ""629 patent describes an electrode array with a first lumen containing electrical conductors and a second lumen adapted to receive a stylet. In contrast, the multicontact electrode array of the present invention requires only one lumen, and thus the fabricating steps described in the ""629 patent differ from those taught by the present invention. Moreover, the ""629 patent teaches that notches must be formed in the lead body to position the electrode members, whereas the present invention does not require such notches.
Other implantable electrodes, electrode arrays, and features of implantable electrodes are taught, e.g., in U.S. Pat. Nos. 5,097,843 (a porous electrode); 5,267,564 (a built-in sensor); 5,423,763 (a suture sleeve for anchoring the lead body); 5,447,533 (a combination electrode and drug delivery system); 5,466,253 (a crush resistant multiconductor lead body); 4,819,647 (a spirally-shaped electrode array); 5,833,714 (electrodes made from tantalum); 6,112,124 (electrodes separated by dielectric partitions or fins); 6,070,105 (modiolus-hugging electrodes for insertion into the cochlea); and 6,129,753 (electrode array with contacts on medial side for insertion into cochlea). Still other electrodes are taught in U.S. Pat. Nos. 4,284,856; 4,357,497; and 6,125,302; or in PCT Publication WO 00/71063A1. The materials from which an implantable electrode array is made in accordance with the teachings of these patents, including many of the manufacturing techniques disclosed in these patents, may also be used with the present invention. For that reason, the patents listed in this paragraph are incorporated herein by reference.
Despite the various types of implantable electrode arrays known in the art, significant improvements are still possible and desirable, particularly relating to reducing costs and providing a more reliable construction based on new manufacturing technology.
Most designs of electrodes and connectors, for example, are based on the principle of molding a contact or array of contacts, usually made from biocompatible metal, into a polymer carrier, such as silicone or polyurethane rubber. The electrode contacts are usually required to be located in a controlled position in reference to the surface of the carrier, with specified surface areas to be fully exposed to the stimulated or interconnection area. Disadvantageously, making such electrodes or connectors becomes extremely difficult, especially when the contacts are very small and/or a large number of contacts are required. One of the main problems encountered in the fabrication of such electrodes or connectors is to find a reliable method of holding the system of contacts in the desired and stable position during the process of welding connecting wires and during the process of molding the polymer carrier. A further problem relates to maintaining a controlled surface of the contacts that are to remain exposed, i.e., to ensure that the contacts are not covered by the polymer when the carrier is molded.
It is thus seen that there is a continual need for improved, more reliable, implantable multicontact electrode arrays that are simpler to make and less costly to make.
The present invention addresses the above and other needs by providing a simple and reliable method of constructing a multicontact electrode array.
The present invention focuses on the construction of the distal end of the electrode array where the electrodes are positioned in a specified spaced-apart relationship.
The invention disclosed and claimed herein provides a simple and reliable method of construction for a multicontact electrode array. Advantageously, during the construction of such electrode, a central lumen is formed in the electrode array lead body. This lumen serves the purpose of providing access for a stylet to be used in conjunction with the lead during implantation of the electrode to the stimulating area. The electrode array may be constructed to have various ring contacts, partial rings, or radially spaced pattern of small contacts of any shape. Depending on the application for which the electrode array is to be used, e.g., brain stimulation, neural stimulation, or spinal cord stimulation the number of contacts will vary. Most of the electrode arrays used for such applications employ between 4 and 16 electrodes, and the arrangement of the electrodes can vary. For example one known arrangement is the paddle type electrode array. Electrodes of the paddle type array, are arranged in two or more parallel columns, permitting stimulation to be driven across an adjacent electrode. Another type of known arrangement positions the electrodes in a row, or xe2x80x9cin line,xe2x80x9d along the longitudinal axis of a small diameter lead body. This in-line electrode arrangement allows the array to be inserted into the stimulating area, in a minimally invasive procedure, through the use of a large diameter needle and through the guidance of a stylet inserted in the lumen of the electrode array.
The present invention is directed to an electrode array wherein the electrodes are organized in a row, xe2x80x9cin line,xe2x80x9d or in a radially placed pattern of small contacts of any shape, and more particularly to a method of construction for making such electrodes. The simplified construction method provided by the invention advantageously reduces material costs, simplifies manufacturing processes, and thus reduces manufacturing time and labor costs.
The method of making an electrode array in accordance with the present invention includes, as an initial step, winding insulated lead wires around a suitable mandrel forming a helix configuration. Helically-wound wire may also be purchased from a vendor. Next, a non-conductive silicone tube jacket is placed around the wound wires exposing the distal lead ends of each insulated wire. A welding process is then used to bond each lead wire tip to a corresponding contact which has been preassembled by resistance welding to a metal foil, e.g., iron foil, structural carrier. The electrode array is then molded after drawing it through a die. The excess foil material at the distal tip is then trimmed, and a heat-shrink tube is placed around the assembled electrode array to prevent leakage of an injected polymer through the small gap of the joining longitudinal line of the foil carrier. The electrode array is then injected with a polymer material to fill any gaps between the lead wires and contacts. To avoid filling the central lumen with the polymer filler material, a central core or stylet is temporarily placed inside the lumen. The heat-shrink tube is then mechanically removed. The construction method is finalized by inserting the preassembled electrode array into a hot acid mixture which etches away the iron foil exposing the contacts at the surface of the electrode array.
The construction method of the present invention is more simplified than others known in the art, and hence provides a more reliable construction method with higher yield rates. All this, in turn, lowers the overall cost to manufacture the multicontact electrode array.